The Role of Molecular Vibrations in the Spin Crossover Phenomenon

Tuchagues, Jean‐Pierre; Bousseksou, Azzedine; Molnár, Gábor; McGarvey, John J.; Varret, F.

doi:10.1007/b95423

Cited by 60 publications

(70 citation statements)

References 63 publications

(99 reference statements)

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Section: Hhhhllh Isomersmentioning

confidence: 99%

“…The importance of the molecular vibrations for the spin crossover phenomenon is generally recognized [46]. The vibrational contribution to the entropy, which can be derived from vibrational spectra and DFT calculations [30,[46][47][48] is not only the additional driving force of the spin transition. Additionally, low energy phonons contribute to the cooperativity as suggested by theoretical considerations based on the Ising model [49] and on elasticity theory [50].…”

Section: Hhhhllh Isomersmentioning

confidence: 99%

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Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study

et al. 2016

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Abstract:The nuclear inelastic scattering signatures of the low-spin centers of the methanosulphonate, tosylate, and perchlorate salts of the spin crossover polymer ([Fe(II)(4-amino-1,2,4-triazole) 3 ] 2+ ) n have been compared for the low-spin phase, for the mixed high-spin and low-spin phases, as well as for Zn(II) diluted samples. Within this series a change in the vibrational pattern in the 320-500 cm´1 region is observed. Significant shifts and decreasing intensity of bands at~320 cm´1 and bands over 400 cm´1 are observed as the molar fraction of the low-spin (LS) centers decrease. Density functional theory calculations using Gaussian09 (B3LYP/CEP-31G) for pentameric, heptameric, and nonameric model molecules yielded the normal modes of several spin isomers: these include the all high-spin (HS) and the all low-spin (LS) configuration but also mixtures of LS and HS centers, with a special focus on those with LS centers in a HS matrix and vice versa. The calculations reproduce the observed spectral changes and show that they are caused by strain extorted on a LS Fe(II) center by its HS neighbors due to the rigid character of the bridging aminotriazole ligand. Additionally, the normal mode analysis of several spin isomers points towards a coupling of the vibrations of the iron centers of the same spin: the metal-ligand stretching modes of the all LS and the all HS spin isomers reveal a collective character: all centers of the same spin are involved in characteristic normal modes. For the isomers containing both LS and HS centers, the vibrational behavior corresponds to two different subsets (sublattices) the vibrational modes of which are not coupled. Finally, the calculation of nuclear inelastic scattering data of spin isomers containing a ca. 1:1 mixture of HS and LS Fe(II) points towards the formation of blocks of the same spin during the spin transition, rather than to alternate structures with a HS-LS-HS-LS-HS motif.

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Section: Hhhhllh Isomersmentioning

confidence: 99%

Section: Hhhhllh Isomersmentioning

confidence: 99%

Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study

et al. 2016

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“…Internal ligand modes are also influenced by the change of the iron-ligand bond length and can be used as probe of spin conversion as well. 34 Thermal spin crossover is an entropy-driven transition from the populated LS state at low temperatures to the HS state, populated at higher temperatures, and is possible when the zero-point energy difference between the HS and LS states (?H HL ) is small, typically of the order of 0-1000 cm −1 . 35,36 An important parameter to characterize the temperature-driven SCO is the transition temperature (T 1/2 ), which corresponds to the temperature at which the LS and HS states are equally populated.…”

Section: Introductionmentioning

confidence: 99%

Computational approach to the study of thermal spin crossover phenomena

Rudavskyi

Sousa

Graaf

et al. 2014

The Journal of Chemical Physics

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The key parameters associated to the thermally induced spin crossover process have been calculated for a series of Fe(II) complexes with mono-, bi-, and tridentate ligands. Combination of density functional theory calculations for the geometries and for normal vibrational modes, and highly correlated wave function methods for the energies, allows us to accurately compute the entropy variation associated to the spin transition and the zero-point corrected energy difference between the low-and high-spin states. From these values, the transition temperature, T 1/2 , is estimated for different compounds.

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“…Raman spectroscopy can be used to monitor the spin state of the material as a function of both temperature and pressure [17], with the intensities of selected "marker" peaks used to follow the SCO. The spectra of 1 at 273, 178 and 103 K (Figure 2a) clearly reflect the significant structural changes that occur during SCO.…”

Section: Variable Temperature and Pressure Raman Spectroscopymentioning

confidence: 99%